Bad idle and sputtering when hot

AeroCoupe said:

There is your problem. You need a chip and a dyno tune to fix that mess. Stock ECU for a mass air car is programmed for a stock 302 with a 55mm MAF, 58mm TB, 19 lb/hr injectors, etc. You can change the heads, cam, and intake and properly tuned it will run fine. Once you change the amount of fuel going in (larger injectors) or the amount of air through the MAF (larger size) it cannot compensate unless you are using a MAF that is calibrated for those injectors. Then when you couple more cubic inches it just throws too much at it and it cannot compensate.

So your choice is to either grab something like an SCT chip and get to a dyno with a tuner that knows these older systems or go stand alone and dive into the deep end of the pool.

Also, do you have an adjustable fuel pressure regulator? Other thing I will say is that you may not have enough injector but that depends on the camshaft and rpm range you want to run. I have a 331 and run 42's as it needs a lot of fuel up past 5,000 rpm.

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AeroCoupe said:

Get a chip and a tune. The car is in open loop when started and after a set time it goes into closed loop. Open loop means it ignores the O2 sensors and closed loop it reads and adjusts off the O2 sensors.

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AeroCoupe said:

Have you checked your air fuel ratio as I would think it would be lean. Only say this as the old 306 in my Coupe ran out of fuel with the 24’s so I dropped 42’s in and got it retuned and gained hp and torque across the curve. My current 331 is running off the same 42’s with a different tune as it was horribly lean on the 306 tune.

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AeroCoupe said:

Have you checked your air fuel ratio as I would think it would be lean. Only say this as the old 306 in my Coupe ran out of fuel with the 24’s so I dropped 42’s in and got it retuned and gained hp and torque across the curve. My current 331 is running off the same 42’s with a different tune as it was horribly lean on the 306 tune.

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